Scientists have revealed that in some exotic states of matter, heat can behave like sound and bounce back and forth. The phenomenon is not new and is known as “second sound.” But MIT scientists have captured images of the “second sound” for the first time.
The images show how heat can move as sound waves when generated within a superfluid, a state of matter in which atoms flow without any friction. Physicists discovered that heat and matter can “collide” with each other, creating oscillations similar to sound waves.
Richard Fletcher, assistant professor of physics at MIT and co-author of the study, was quoted as saying in media reports: “It’s like you have a tank of water and half of it is about to boil.”
“If you then look, the water itself may seem totally calm, but suddenly the other side is hot, and then the other side is hot, and the heat comes and goes, while the water seems still,” he added.
The study, published in Science, can help physicists determine how heat behaves in superfluids and other related materials, such as superconductors and neutron stars.
“There are strong connections between our puff of gas, which is a million times thinner than air, and the behavior of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars,” says Martin Zwierlein, professor by Thomas A. Frank. MIT physicist and research team leader.
“We can now seamlessly test the temperature response of our system, which teaches us things that are very difficult to understand or even achieve,” he adds.
How was the experiment carried out?
The scientists used a group of lithium-6 atoms, fermions that normally repel each other. By cooling the atoms near absolute zero and implementing a magnetic field, they caused the atoms to pair up and generate a superfluid.
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Using a laser beam, they generated a hot spot within the superfluid and used another laser beam to capture the resulting heat patterns.
Their observations revealed that the heat patterns exhibited periodic motion similar to sound waves, but were not synchronized with matter waves, indicating an oscillation in opposite directions for heat and matter. This phenomenon, known as second sound, differs from ordinary sound in that heat and matter move together.
(With contributions from agencies)